Nailing machine

ABSTRACT

A pneumatic, linear thrust hand tool, such as a nail driver wherein a charge of pressurized gas in a firing chamber acts, when a main valve is opened, to drive a ram downward. The main valve is opened by a higher pressure source gas entering a charging chamber under a piston carried on the valve stem. Then a control valve is released, the pressurized gas under the piston is delivered to the main cylinder to return the ram and, when the main valve is closed, the pressure in the firing chamber is equalized with that in the charging chamber to prepare it for the next &#34;firing&#34;.

BACKGROUND OF THE INVENTION

Most pneumatic tools are cumbersome to handle and require an aircompressor or other source of large quantities of pressurized gas. As aresult, they also require lengthy hoses to minimize required movement ofthe air compressor.

OBJECTS OF THE INVENTION

It is an object of this invention to provide a pneumatic hand tool whichis convenient to handle and which effects efficient use of availablepressurized gas.

It is a further object of this invention to provide a pneumatic handtool which can operate efficiently and at length on a small container ofpressurized gas.

Other objects and advantages of this invention will become apparent fromthe description to follow, particularly when read in conjunction withthe accompanying drawing.

SUMMARY OF THE INVENTION

In carrying out this invention, I provide a cylinder with a ram thereincarrying a plunger to apply a linear thrust, as to drive a nail. A largevalve to one end of the cylinder opens to a firing chamber containing acharge of pressurized gas. The valve is opened by a valve actuatorpiston which is slidable in a cylinder wholly contained within another,charging chamber above the firing chamber. When a control valve isoperated, gas from a source is introduced under the piston and, afterthe piston lifts the valve off its seat, the gas flows around the pistonto fill the charging chamber. Then, when the trigger is released, thecontrol valve moves to its normal position wherein the gas previouslytrapped below the main valve actual piston is released and directed tothe main cylinder below the ram to return it to its starting position.Then, when the main valve is closed, a pressure equalizing valvecontained in the main valve stem equalizes pressures in the charging andfiring chamber. Hence, a single charge of the source gas is used to openthe valve; to return the ram to a starting position; and then to chargethe firing chamber.

BREIF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a section view of a pneumatic hand tool embodying features ofthis invention;

FIG. 2 is a partial section view of the tool in another stage ofoperation;

FIG. 3 is a partial section view of an alternative control for thepneumatic tool.

DESCRIPTION OF PREFERRED EMBODIMENTS The Embodiment of FIGS. 1 and 2

Referring now to FIGS. 1 and 2 with greater particularity, the nail gun10 of this invention includes a nail discharge barrel 12 for positioninga nail for driving, a nail cartridge 14, a power cylinder 16, and adriving ram 18, which is reciprocable in the cylinder and carries aplunger 19. The power cylinder 16 is normally closed by a poppet valve20 between it and a firing chamber 23, as shown in FIG. 1. Carried onthe stem 22 of the poppet valve 20 is an actuator piston 24 which, whendriven upward, raises the poppet valve 20 off of its seat. The actuatorpiston 24 is reciprocable in an open top, shallow cylinder 26 havingby-pass grooves 25 near the upper end thereof. The open top cylinder 26is contained within a high pressure or charging chamber 28. The volumeof the high pressure chamber 28 can be adjusted by threading anadjustment wheel 30 to move a top closure 32 up and down as desired. Acheck valve 34 in the top closure allows pressure fluid in the chamber28 to move above the top closure 32 to balance pressure and facilitateadjustment by the control knob 30.

Carried on the gun 10 is a suitable source of pressure fluid such as acylinder 36 of a high pressure gas. The supply gas may, for example, bebottled carbon dioxide at, say 750 p.s.i., or in the alternative, theremay be a hose connection from a remote source of pressure such as an aircompressor. In any event, the high pressure gas is delivered throughducts 38 contained in the gun handle 40 and then through tubing of anevaporator coil 42 to the intake 44 of a spool control valve 46. Beforeentering the control valve 46, the gas passing through the evaporatorcoil 42 absorbs heat from the surroundings or from a fitted heat source48, such as a butane lighter or the like.

In the position of the spool 46 shown in FIG. 1, prior to pressing thetrigger 50, the high pressure gas inlet 44 is shut off by the spool 46and the main poppet valve 20 is seated. At this stage the charging andfiring chambers 28 and 23 are at the same pressure, being equalizedthrough passage 52 in the wall 53 separating the chambers, and through aduct 54 through the valve stem 22 opening into the intermediate orworking chamber 23. Of course, since the same quantity of fluidpreviously in the charging chamber 28 now occupies both chamber 23 and28, it is at a pressure lower than source, e.g. 250 p.s.i. Only when themain valve 20 is closed are the ducts 52 and 54 in alignment. Hence thevalve stem 22 is, itself, a supply valve for the intermediate pressureor firing chamber 23. When the main valve 20 is closed, pressure fluidin the upper charging chamber 28 flows to the lower firing chamber toload it for the next "firing".

A small bypass duct 56 from the inlet passage 44 biases the controlvalve spool 46 to its downward position. When in that position, thespace below the main valve actuator piston 24 is balanced through ports58 and 60 with the pressure below the drive ram 18 at near atmosphericpressure with the ram fully raised. The space above the ram 18 is opento atmosphere at 62 through duct 64.

When the trigger is pressed and valve spool 46 is raised to the positionshown in FIG. 2, the high pressure gas inlet 44 is opened to the spacebelow the main valve actuator piston 24 raising it, and with it thevalve stem 22, to raise the main valve 20 off of its seat. This producesa rush of fluid from the firing chamber 23 into the main drive cylinder16 to force the ram 18 down. When the actuator piston 24 nears the topof its stroke, the bypass grooves 25 in the shallow cylinder 26 allowthe high pressure gas to blow by the piston 24 and pressurize the highpressure chamber 28 to a level close to source pressure, e.g. about 750psi.

In the meantime the main drive cylinder 16 below the piston is vented tothe atmosphere at 62 through passage 63 and port 60, and the port 64below the main valve 20 is closed off by the valve spool 46. Hence, thedrive ram 18 continues down by reason of the pressure differentialacross it until, finally, the remaining kinetic energy is absorbed inthe bumper 66 at the lower end of the cylinder 16.

When the trigger 50 is released, the spool 46 is returned to its lowerposition by reason of the biasing pressure in bypass duct 56. The highpressure gas in the shallow main valve actuator cylinder 26, which wastrapped below the control piston 24 is now released through ports 58 and60 and conducted through line 63 to the main drive cylinder 16 below theram 18, driving it back up to its original position shown in FIG. 1. Therelease of pressure previously trapped below the actuator piston 24allows the piston to be driven down by the pressure fluid above it incharging chamber 28 carrying the main valve 20 with it to return to itsseat. This again opens the equalizing passages 52 and 54 to bring thepressure in the charging and firing chambers 23 and 28 into equalizationat the intermediate level, thus preparing the gun for the nextoperation.

Summarizing, when the valve spool 46 is raised by pressing the triggerthe high pressure gas from the source 36 enters under the main valveactuator piston 24 to lift the main valve 20 and cause intermediatepressure in the firing chamber 23 to drive the ram 18 and plunger 19downward. Then when the actuator piston reaches the level of the by-passgrooves 25, the high pressure fluid escapes around the piston 24 tocharge the entire charging chamber 28. Now, when the trigger 50 isreleased and the valve spool 46 is lowered by pressure in the passage56, that portion of the high pressure fluid below the actuator piston 24is released through passage 58 to allow the high pressure fluidremaining in the upper chamber to drive the actuator piston 24 down tothe position shown in FIG. 1, wherein the pressures in chambers 28 and23 are then equalized, through passages 52 and 54, to an intermediatepressure level. This sets the pressure conditions for the next "firing".

In the meantime, the high pressure fluid that was exhausted from belowthe control piston 24 is delivered through passage 60 to the maincylinder 16 below the ram 18, while the same cylinder above the ram 18is exhausted through passages 63 and 62 to the atmosphere. This drivesthe ram upward to the position shown in FIG. 1 and sets the mechanismfor the next "firing".

Hence a single charge of high pressure fluid opens the main valve 20 asit charges the chamber 28. Then a portion of it returns the ram 18 tostarting position while the remainder loads the firing chamber for thenext strike.

As an additional feature of this invention, I provide a device 68 toavoid wasting the first nail for lack of adequate pressure. In order tofill the intermediate chamber 23 with gas at an adequate pressure todrive a nail N, it may require that the trigger be actuated to fire thegun at least once. The blocking device at 68 includes a spring member 70which holds the nails retracted into the nail feed device 14 unless thepressure in the chamber 23 is high enough to drive the nail properly. Apiston 72 biases against the spring 70 under the pressure in chamber 23by reason of sensing passageway 74. Hence, when the pressure in thefiring chamber 23 reaches a sufficiently high level, the piston 72 willretract the spring member 70 and allow a nail to move into place.

The Embodiment of FIG. 3

Referring now to FIG. 3 the tool is here conditioned as a hammeringdevice. In so adapting it, the ram 18 is replaced by a similar ram whichis proportioned for hammering rather than nail driving and the nail feeddevice 14 would be removed.

In this arrangement, a simple on-off valve 76 is adapted so as to beactuated by the trigger 50, the valve being normally biased towardclosed position by supply gas entering through passageway 38a from thepressure source 36.

A passageway 80 opening from high pressure charging chamber 28 biasesthe control valve spool 46 downward while supply pressure enterschambers 81 below the valve spool 46, when the trigger valve 76 is open,to bias it upward toward the position shown in FIG. 3.

In operation, squeezing the trigger 50 to open the valve 76 permits gasfrom the source 36 to enter into the chamber 81 below the valve spool46. This pressure is sufficient to overcome the opposing pressure inchamber 80, at the level of the charging chamber 28, because at thisinstant, the pressure in chamber 28 has been reduced to equalize chamber23 through the ducts 52 and 54. Thus, high gas pressure in the lowerchamber 81 forces the valve plunger upward to its top position (as shownin FIG. 3) causing the valve actuator 24 to lift the main valve 20 andforce the ram 18 to move downward at a high speed, as in the nailingoperation described in connection with FIGS. 1 and 2. Then, as thepressure in the upper chamber 28 increases it reaches the magnitude ofthe supply gas, causing the valve spool 46 to move back down to itslower position, because of the unequal areas at the two ends of thevalve spool 46 with the guide plunger 47 at only one end. This initiatesthe return stroke of the ram 18 as in the nailing operation.

The device is now ready for its second stroke, and if the trigger isheld squeezed, the second stroke will occur as soon as the valve hascompleted its downward movement. The ram 18 will thus reciprocate at arate resulting from a proper combination of mass of the moving parts andresistence to gas flow in the several passages.

While this invention has been described in conjunction with preferredembodiments thereof, it is obvious that modifications and changestherein may be made by those skilled in the art without departing fromthe spirit and scope of this invention, as defined by the claimsappended hereto.

Having described my invention, I claim:
 1. A pneumatic linear thrusthand tool comprising:a main cylinder; a ram reciprocable in said maincylinder; a firing chamber above said main cylinder; a large main valveoperable when opened to bring said main cylinder and said firing chamberinto communication; a charging chamber; supply valve means for bringingsaid charging and firing chambers into communication when said mainvalve is closed; control valve means operative in one position toconnect said charging chamber to a source of pressurized gas; and, amain valve actuator operative in response to flow of gas into saidcharging chamber to open said main valve.
 2. The pneumatic hand tooldefined by claim 1 wherein the said valve actuator comprises:an actuatorcylinder contained within said charging chamber; an actuator pistonreciprocable in said actuator cylinder; charging ports in said actuatorccylinder opening to the interior of said charging chamber; saidcharging ports being uncovered by said actuator piston at the outerportion of its stroke; conduit means for delivering pressurized gas tosaid charging chamber through a port at one end of said actuatorcylinder to drive said actuator piston through said stroke; meansstructurally connecting said actuator piston to said main valve to opensame through said stroke.
 3. The pneumatic hand tool defined by claim 2wherein said last-named means comprises:a passageway interconnectingsaid charging and firing chambers; a valve stem slidable in saidpassageway and interconnecting said main valve and said valve actuatorpiston; a first duct opening from said charging chamber to saidpassageway; a second duct on said valve stem opening from saidpassageway to said firing chamber, said first and second ducts being incommunication when said main valve is closed.
 4. The pneumatic hand tooldefined by claim 2 wherein:said control valve means is operative in asecond position to connect said one end of the actuator cylinder to saidmain cylinder below said ram.
 5. The pneumatic hand tool defined byclaim 1 wherein:said control valve member is operative in said secondposition to connect the said main cylinder above said ram to atmosphere.6. The pneumatic hand tool defined by claim 1 including:means foradjusting the size of said charging chamber.
 7. The pneumatic hand tooldefined by claim 1 including:a hand-operated trigger operativelyassociated with said control valve: said control valve being moved tosaid one position by actuating said trigger; and including: meansbiasing said control valve towards said other position.
 8. The pneumatichand tool defined by claim 1 including:a control valve cylinder; saidcontrol valve being reciprocable in said cylinder; duct means connectingone end of said cylinder to the source of pressurized fluid and theother end of said cylinder to said charging chamber; said one end ofsaid control valve being smaller in area than said other end so thatwhen pressures therein are substantually equal said control valve willbe biased towards said one position but said differential areas can beovercome by pressure differential when said supply valve is opened tobring the pressure of the charging chamber down to the level of saidfiring chamber.
 9. The pneumatic hand tool defined by claim 1including:a plunger carried by said ram; a nail guide passage at thelower end of said tool for receiving said plunger; a nail cartridge forfeeding a supply of nails to said nail passage way.